Melatonin is one impressive hormone. Not only does it send sleepy-time signals to your body, but it also has antioxidant and anti-inflammatory properties that can benefit mitochondrial function and even skin health. Not to mention, melatonin plays a role in fertility: "One of the richest sites of melatonin in the body is the ovaries," midwife and integrative medicine doctor Aviva Romm, M.D., says on the mindbodygreen podcast. "And fertility actually depends on healthy melatonin levels in the brain and in the ovaries."
Again, melatonin is a workhorse that you'll want to make sure you have enough of. Your brain (pineal gland) naturally produces the majority of endogenous melatonin. But when it comes to taking melatonin supplements (i.e., exogenous melatonin), some concerns do arise: There's the dosage point—where some research suggests that taking too much melatonin over time may adversely affect other hormones—and there's a much sneakier hitch Romm says is important to keep in mind.
Apparently, melatonin can contribute to weight gain—depending on what time you take it.